Context Ceftriaxone, an expanded-spectrum cephalosporin,
is an antimicrobial agent commonly used to treat severe
Salmonella infections, especially in children. Ceftriaxone-resistant
Salmonella infections have recently been reported in the United States,
but the extent of the problem is unknown.
Objectives To summarize national surveillance data for
ceftriaxone-resistant
Salmonella infections in the United States
and to describe mechanisms of resistance.
Design and Setting Case series and laboratory evaluation
of human isolates submitted to the Centers for Disease Control
and Prevention from 17 state and community health departments
participating in the National Antimicrobial Resistance Monitoring
System (NARMS) for enteric bacteria between 1996 and 1998.
Patients Patients with ceftriaxone-resistant
Salmonella infections between 1996 and 1998 were interviewed and isolates
with decreased ceftriaxone susceptibility were further characterized.
Main Outcome Measures Exposures and illness outcomes,
mechanisms of resistance.
Results The prevalence of ceftriaxone-resistant
Salmonella was 0.1% (1 of 1326) in 1996, 0.4% (5 of 1301) in 1997, and
0.5% (7 of 1466) in 1998. Ten (77%) of the 13 patients with
ceftriaxone-resistant infections were aged 18 years or younger.
The patients lived in 8 states (California, Colorado, Kansas,
Massachusetts, Maryland, Minnesota, New York, and Oregon). Nine
(82%) of 11 patients interviewed did not take antimicrobial
agents and 10 (91%) did not travel outside the United States
before illness onset. Twelve of the 15
Salmonella isolates with
ceftriaxone minimum inhibitory concentrations of 16 µg/mL
or higher were serotype Typhimurium but these isolates had different
pulsed-field gel electrophoresis patterns. Thirteen of these
15 isolates collected between 1996 and 1998 were positive for
a 631base pair polymerase chain reaction product obtained
by using primers specific for the
ampC gene of
Citrobacter freundii.
Conclusions Domestically acquired ceftriaxone-resistant
Salmonella has emerged in the United States. Most ceftriaxone-resistant
Salmonella isolates had similar AmpC plasmid-mediated resistance.
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